ELSA GLADIAC 511, Руководство пользователя

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Graphics know-how
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| ELSA GLADIAC 5II |
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EN
4.3 Color palettes, TrueColor and gray scales
Common graphics modes are listed in the following table. Not all graphics
modes are available on the ELSA boards:
4.3.1 VGA
In VGA graphics boards, the digital color information stored in the video
memory (4 bits for 16 colors or 8 bits for 256 colors) is converted into a digital
18-bit value in the graphics adapter in a CLUT (ColorLookUpTable). The 3 x 6
bits are converted separately for R/G/B (red/green/blue) in the RAMDAC (D/
A converter) and transferred to the monitor as analog signals on just three
lines (plus sync lines). The original color values are converted into completely
different values by means of a translation table. The value stored in the video
memory is thus not a color value, but only a pointer to a table in which the
actual color value is found. The advantage of this method: Only 8 bits need to
be stored for each pixel, although the color values are 18 bits wide; the
disadvantage: Only 256 colors can be displayed simultaneously from a
palette of 262,144 possible colors.
4.3.2 DirectColor
The situation is different in the case of DirectColor (TrueColor, RealColor and
HighColor). In this case, the value stored in the video memory is not trans-
lated but is passed directly to the D/A converter. This means that the full
Graphics
mode
bpp bpg
Colors
(from palette) Max. gray levels
VGA 0x12
VGA 0x13 4
8 6+6+6
6+6+6 16 of 262,144
256 of 262,144
16
64
Standard 8
8 6+6+6
6+6+6 256 of 262,144
256 of 16.7 million
64
256
HighColor 15
16
16 5+5+5
6+6+4
5+6+5 32,768
65,536
65,536 32
16
32
TrueColor 24
32 8+8+8
8+8+8+8
16.7 million
16.7 million 256
256
(bpp = bits per pixel; bpg = bits per gun)